Ceramic heaters, a method for producing the same and heating apparatuses used for a system for producing semiconductors

ABSTRACT

An object of the present invention is to provide a novel ceramic heater having a ceramic substrate with a heating face and a heat generator so that the temperature on the heating face may be controlled without the necessity of a temperature controlling member separate from the substrate. A ceramic heater  1 B has a ceramic substrate  2  with a surface  2 A and a heat generator  3.  The surface  2 A includes a heating face  2   a,  a first region  15  provided out of the heating face  2   a  and a second region  13  provided out of the heating face  2   a.  The second region  13  has an emissivity of thermal radiation lower than that of the first region  15.

[0001] This application claims the benefit of Japanese PatentApplication P2001-352964, filed on Nov. 19, 2001, the entirety of whichis incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to ceramic heaters, a process for producingthe same, and heating apparatuses for a system for producingsemiconductors.

[0004] 2. Related Art Statement

[0005] In a system for producing semiconductors, a ceramic heater hasbeen provided for heating a wafer (substrate) so as to deposit asemiconductor thin film on the wafer from gaseous raw materials such assilane gas by means of thermal CVD or the like. In such heater, it isnecessary to maintain the temperature on a heating face high and toassure the uniformity of the temperature on the heating face so as toprevent semiconductor defects. Such ceramic heater, however, isgenerally made of a ceramic substrate and a heat generator embedded inthe substrate, so that some degree of temperature difference may beobserved on the heating face.

[0006] Japanese patent publication 6-53, 145 A discloses a technique forimproving the uniformity of temperature on the heating face for asemiconductor of a ceramic heater. That is, a disk-shaped ceramic heaterwith a heating face for a semiconductor is produced. The temperaturedistribution on the heating face is then observed with a thermograph.The thus observed temperature distribution is then subjected to imageprocessing to obtain image-processed data. A reflector is provided on aposition opposing the back face of the ceramic heater. Heat radiatedfrom the back face of the ceramic heater is reflected by the reflectorand irradiated into the heater again. The temperature distribution ofthe reflector is controlled based on the image-processed data. In aregion where a lower temperature is observed on the heating face, thethermal absorptance of the reflector is reduced, so that heat reflectedby the reflector into the heater may be increased. The temperature inthe region with a lower temperature observed may be thus increased. Thesurface of the reflector is subjected to sandblasting to control thesurface roughness and thus to control the reflectance of the reflector.

SUMMARY OF THE INVENTION

[0007] The inventor has studied the above technique in Japanese patentpublication 6-53, 145 A and encountered the following problems. That is,it is necessary to fix a reflector on a specific position opposing theback surface of a ceramic heater in a semiconductor chamber. Afterfixing the reflector, the distribution of the thermal absorptance (orthermal reflectance) on the reflecting face of the reflector should beaccurately matched with the temperature distribution on the heating faceof the ceramic heater before fixing the reflector. It is howeverdifficult to adjust the positions of the heating face of the heater andof the reflecting face of the reflector, according to the followingreasons.

[0008] (1) The center of a circular heating face of the ceramic heatershould be accurately matched with the center of the circular reflectingface of the reflector.

[0009] (2) In addition to this, the angle and diameter of each positionof the heating face with respect to the center should be accuratelymatched with those of each position of the reflecting face with respectto the center.

[0010] Furthermore, even if such adjustment of two-dimensional positionhad been successfully performed, such adjustment is insufficient forobtaining uniformity of temperature on the heating face within aspecification, according to the following reasons. That is, the distancebetween the back face of the heater and the reflecting face of thereflector is also important. Specifically, the thermal absorptance ofeach point on the reflecting face is calculated and designed on theprovision that a distance between the reflecting face and the back faceof the heater is a specific value “α”. When the distance between thereflecting face and back face is smaller than “α”, heat transmitted fromthe reflecting face to the back face of the heater is increased so thatthe temperature on the heating face of the heater may be increased. Thefollowing adjustments (3) and (4) are thus needed.

[0011] (3) To control the distance between the back face of the heaterand the reflecting face of the reflector at a specific value “α”.

[0012] (4) To make the back face of the heater and the reflecting facebe parallel with each other over the whole of the back face.

[0013] It may be difficult to set and fix the reflector in asemiconductor chamber while maintaining the above four geometricalconditions.

[0014] Furthermore, the fixed reflector may result in a complicatedstructure as well as the deterioration of the reflector, fracture orwarping of the reflector due to thermal stress and adverse effects ongas flow.

[0015] An object of the present invention is to provide a novel ceramicheater having a ceramic substrate with a heating face and a heatgenerator so that the temperature on the heating face may be controlledwithout the necessity of a temperature controlling member separate fromthe substrate.

[0016] The present invention provides a ceramic heater having a heatgenerator and a ceramic substrate with a surface including a heatingface. A first region is provided on the surface and out of the heatingface, and a second region is provided on the surface and out of theheating face. The second region has an emissivity of thermal radiationlower than that of the first region.

[0017] The present invention further provides a heating apparatus for asystem for producing semiconductors. The heating apparatus has theceramic heater with a back face, a terminal connected with thegenerator, a hollow supporting member defining an inner space and fixedon the back face of the heater, and a power supply means provided in theinner space and electrically connected with the terminal.

[0018] A system for producing semiconductors means a system usable in awide variety of semiconductor processes in which metal contamination ofa semiconductor is to be avoided. Such system includes a film forming,etching, cleaning and testing systems.

[0019] The present invention provides a method for producing a ceramicheater having a heat generator and a ceramic substrate with a surfaceincluding a heating face. The method has the step of providing a firstregion and a second region both on the surface and out of the heatingface. The second region has an emissivity of thermal radiation lowerthan that of the first region.

[0020] The inventor has tried to divide the surface of the ceramicsubstrate itself other than the heating face into a plurality of regionshaving the different thermal emissivities with each other. The inventorhas thus studied the effects on the heating face of the substrate. As aresult, the inventor has found that the uniformity of temperature on theheating face may be substantially affected beyond expectation. Thepresent invention is based on the findings.

[0021] For example, when a cold spot is observed on a heating face of aceramic substrate, an emissivity of thermal radiation may be reduced ina projected area defined by projecting a planar pattern of the cold spotonto the back face. It is thereby possible to slightly increase thetemperature in the cold spot on the heating face so that the cold spotmay be cancelled. Alternatively, when a hot spot is observed on aheating face of a ceramic substrate, an emissivity of thermal radiationmay be increased in a projected area defined by projecting a planarpattern of the hot spot onto the back face. It is thereby possible toslightly reduce the temperature in the hot spot on the heating face sothat the hot spot may be cancelled. Such change or control of theemissivity of thermal radiation of a part of the surface of the ceramicsubstrate may be performed only with a surface processing of the ceramicsurface. It has not been known that the temperature distribution on theheating face may be considerably improved only by performing surfaceprocessing of the ceramic substrate to control the emissivity of thermalradiation.

[0022] These and other objects, features and advantages of the inventionwill be appreciated upon reading the following description of theinvention when taken in conjunction with the attached drawings, with theunderstanding that some modifications, variations and changes of thesame could be made by the skilled person in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a schematic diagram for explaining a method formeasuring the temperature distribution on a heating face 2 a of aceramic heater 1.

[0024]FIG. 2 (a) is a plan view showing the ceramic heater 1 observedfrom the side of heating face 2 a.

[0025]FIG. 2 (b) is a cross sectional view showing a proximal part of aside face 2 c of the heater 1.

[0026]FIG. 3 (a) is a bottom view showing a ceramic heater 1A afterlapping observed from the side of a back face 2 b.

[0027]FIG. 3 (b) is a cross sectional view schematically showing aproximal part of a side face 2 c of the heater 1A.

[0028]FIG. 4 (a) is a bottom view showing the heater 1A with a maskmounted thereon observed from the side of a back face 2 b.

[0029]FIG. 4 (b) is a cross sectional view showing a proximal part ofthe side face 2 c of the heater 1A with a mask mounted thereon.

[0030]FIG. 5 (a) is a bottom view showing a ceramic heater 1B after aroughening treatment observed from the side of a back face 2 b.

[0031]FIG. 5 (b) is a cross sectional view showing a proximal part ofthe side face 2 c of a heater 1B.

[0032]FIG. 6 is a perspective view showing a heating apparatus 22observed from the side of a back face 2 b.

[0033]FIG. 7 is a cross sectional view of a heating apparatus 22.

[0034]FIG. 8 (a) is a cross sectional view showing an essential part ofa ceramic heater 1C having a first region 15 with a groove 24 formedtherein.

[0035]FIG. 8 (b) is a cross sectional view showing an essential part ofa ceramic heater 1D having a first region 15 with protrusions formed atspecified intervals thereon.

[0036]FIG. 9 is a cross sectional view showing an essential part of aceramic heater 1E.

[0037]FIG. 10 is an image showing the result of measurement of thetemperature distribution on a heating face of a ceramic heater 1 beforea treatment.

[0038]FIG. 11 is an image showing the result of measurement of thetemperature distribution on a heating face of a ceramic heater 1B aftera treatment.

PREFERRED EMBODIMENTS OF THE INVENTION

[0039] The present invention will be described further in detail,referring to the attached drawings.

[0040] In an embodiment shown in FIGS. 1 to 7, the center line averagesurface roughness of a ceramic substrate is controlled so as to controlthe emissivity of thermal radiation. That is, as the center line averagesurface roughness “Ra” of a ceramic surface is larger (as the ceramicsurface is made rougher), the emissivity of thermal radiation of thesurface is slightly increased. On the contrary, as the center lineaverage surface roughness “Ra” of a ceramic surface is lower (as theceramic surface is made smoother), the emissivity of thermal radiationof the surface is slightly reduced.

[0041] According to one embodiment of the present invention, thetemperature distribution on a heating face of a ceramic heater isobserved. For example, as shown in FIG. 1, the heater has a plate-shapedceramic substrate 2 and heat generators 3A, 3B embedded in the substrate2. 2 a denotes a heating face, 2 b a back face, and 2 c a side face. Ameasuring apparatus 4 is provided over the heating face so that thetemperature distribution on the heating face is measured as an arrow“A”. The results obtained by the measurement is sent as an arrow “B” toa processor 5 to perform image processing. The result of the imageprocessing is then sent to a display 6 as an arrow “C”.

[0042] When a cold spot or hot spot out of a specification is observedon the heating face, the subsequent steps are performed. For example, asshown in FIG. 2(a), it is provided that a cold spot 7 is observed on theheating face 2 a. As shown in FIG. 2(b), it is also provided that thewhole of a side face 2 c and a back face 2 b of the substrate 2 is roughto a some degree, at this stage.

[0043] In the present embodiment, a projected area may be defined atleast on the back face 2 b corresponding with a planar pattern of thecold spot 7. A second region with a smaller center line average surfaceroughness is provided in the projected area. For example, as shown inFIGS. 3(a) and 3(b), 8 denotes a projected area defined by projecting aplanar pattern of the cold spot 8 onto the back face 2 b. For providingthe second region, for example, the whole of the back face 2 b and sideface 2 c of the heater 1A is subjected to lapping so at to formsmoothened surfaces 10A, 10B and 10C each having a smaller center lineaverage roughness.

[0044] As shown in FIGS. 4(a) and 4(b), the side face 2 c is coveredwith a mask 12B. The projected area 8 corresponding with the cold spot 7is also covered with a mask 12A.

[0045] The back face 2 b of the substrate 2 is then subjected to atreatment for increasing surface roughness. The masks 12A and 12B arethen removed to obtain a ceramic heater 1B shown in FIGS. 5(a), 5(b) and6.

[0046] In the heater, the projected area 8 corresponding with the coldspot 7 on the back face 2 b is covered with the mask so that thesmoothened surface 10B remains. The smoothened surface 10A remains onthe side face 2 c of the substrate 2 covered with the mask Thesesmoothened faces 10A and 10B together form a second region 13. The otherregion without the mask on the back face 2 b is made a roughened surface14, which forms a first region 15 with a larger center line averageroughness.

[0047] It has been proved to be possible to reduce or cancel the coldspot, by forming the smoothened surface region 13 with a smaller centerline average surface roughness in the projected area one the back facecorresponding with the cold spot or in the side face.

[0048] Further, it should be noted that the uniformity of thetemperature distribution on the heating face may be realized by surfaceprocessing of the surface itself of a ceramic substrate. Such control ofthe temperature distribution does not require an outer member (such as areflector) fixed outside of the ceramic substrate, for example in theprior art described above.

[0049] Particularly, in the present embodiment, two layers of resistanceheat generators 3A and 3B are embedded in the ceramic substrate so thatthe calorific value generated by each heat generator is controlled forperforming so-called two zone controlling system. It is possible toapply a multi zone control system having three or more zones. In thepresent example, a multi-zone control system, particularly multi-zonecontrol system using a plural layers of heat generators embedded in aceramic substrate, is applied. The temperature distribution on theheating face may be normally controlled within an order of not more than10° C., by applying such multi-zone control system. In an actuallymanufactured article, a local cold spot or hot spot may be observed dueto various reasons, even when the multi-zone control system isperformed.

[0050] In this case, it may be considered to control the calorific valueof a heat generator embedded in a zone where a cold spot or hot spot isobserved, so as to cancel the cold or hot spot. Such control has been,however, proved to be difficult. The reasons are as follows. Whenelectric power supply to each of the heat generators is increased orreduced, the calorific value of the heat generator is changed. Suchchange does not necessarily reduce the temperature distribution on theheating face and may even increase the temperature distribution. Themulti-zone heater is effective for controlling the average temperaturein each of the outer peripheral zone and inner zone of the heating face.However, a cold spot or hot spot may be observed in only a part of eachof the outer peripheral and inner zones of the heating face in a ceramicheater. It is thus difficult for providing a solution for such cold orhot spot.

[0051] The present invention may provide a solution for such local hotor cold spot, even in a small order of, for example, not more than 10°C., when uniformity of temperature distribution has been alreadyrealized to a some degree by means of the multi zone control system. Itis thus possible to control and accurately adjust the temperaturedistribution for an individual article.

[0052] It is possible to provide a reduced temperature distributionaccording to the present invention. The control according to the presentinvention is, however, not limited to such control of reducing thetemperature distribution. For example, a region with a highertemperature or a lower temperature with a specific temperaturedifference may be provided in a specified area on the heating face,according to the present invention.

[0053] An emissivity of thermal radiation on the surface of a ceramicsubstrate may be measured as follows. A ceramic substrate is maintainedat a specific temperature and its surface is observed with athermoviewer to obtain a temperature. The emissivity of thermalradiation is adjusted so that the temperature measured by thethermoviewer becomes identical with a specified temperature for theceramic substrate.

[0054] In the present invention, a plurality of regions having theemissivities of thermal radiation different from each other may beprovided on the surface of a ceramic substrate, by controlling thecenter line average surface roughness, as described above.Alternatively, the regions may be provided according to the followingmethods.

[0055] (1) A recess having a depth of not smaller than 1 μm is formed ina first region by machining. The recess may preferably be an elongaterecess or groove, and most preferably a V-shaped or U-shaped groove. Thedepth of the recess may preferably be not smaller than 10 μm for furtherimproving the effects of the present invention. The depth may preferablybe not larger than 1000 μm on the viewpoint of difficulty of machiningprocess.

[0056] (2) A protrusion having a height of not smaller than 1 μm isformed by machining in a first region. Preferably, the protrusion isso-called an emboss or dimple. The height of the protrusion maypreferably be not smaller than 10 μm for further improving the effect ofthe present invention. The height may preferably be not larger than 1000μm on the viewpoint of the difficulty of machining process and forpreventing the adverse effects on the gas flow used for processing.

[0057] (3) The first region is subjected to a chemical surfacetreatment. Such treatment includes etching or oxidizing process asdescribed below.

[0058] (4) The lightness of the first region is made smaller than thatof the second region, so as to increase the emissivity of thermalradiation of the first region. In this case, the difference of thelightness of the first region and that of the second region maypreferably be not smaller than 0.5. Further, the lightness of the firstregion may preferably be N1 to N6, and the lightness of the secondregion may preferably be N2 to N10.

[0059] Lightness will be described below. The surface color of asubstance may be represented by three properties of color perception:hue, lightness and chroma. Lightness is a property for representingvisual perception judging the reflectance of the surface of a substance.The representations of the three properties are defined in “JIS Z 8721”.The representation of lightness will be briefly described. The lightness“V” is defined based on achromatic colors. The lightness of ideal blackand that of ideal white are defined as “0” and “10”, respectively.Achromatic colors between the ideal black and ideal white are dividedinto 10 categories and represented as symbols from “N0” to “N10”. Thecategories are divided so that each category has a same rate or span interms of visual perception of lightness. When actually measuring thelightness of a ceramic substrate, the surface color of the substrate iscompared with standard color samples corresponding with “N0” to “N10” todetermine the lightness of the body. The lightness is determined to thefirst decimal point, whose value is selected from “0” and “5”.

[0060] In a preferred embodiment, a difference between the maximum andminimum temperatures on the heating face of the substrate is not morethan 20° C. and more preferably not more than 10° C. when an averagetemperature on the heating face is 600° C. When the average temperatureon the heating face is not lower than 600° C., the effect of thermalradiation from a rough surface becomes considerable. As a result, theinvention may be effective for further improving the uniformity oftemperature after the in-plane temperature distribution of an object onthe heating face is controlled to be uniform to a some degree.

[0061] According to one embodiment of the present invention, a ceramicsubstrate has a surface including at least a heating face and a backface opposing to the heating face. Further, the surface of the substratemay include a side face in addition to the heating and back faces.

[0062] In a preferred embodiment, the back face of the substrate isdivided into first and second regions. The first region has anemissivity of thermal radiation larger than that of the second region.The temperature on the heating face may be slightly reduced in a firstprojected area defined by projecting the first region onto the heatingface, because the first region has a larger emissivity of thermalradiation. The temperature on the heating face may be slightly increasedin a second projected area defined by projecting the second region ontothe heating face, because the second region has a smaller emissivity ofthermal radiation.

[0063] Further, a first or second region may be provided on the sideface of the substrate. When a cold spot is observed in the outerperipheral portion of the heating face, the side face may be made thesecond region having a smaller emissivity of thermal radiation, so thatthe temperature in the cold spot may be increased to cancel the coldspot. Alternatively, when a hot spot is observed in the outer peripheralportion of the heating face, the side face may be made the first regionhaving a larger emissivity of thermal radiation, so that the temperaturein the hot spot may be reduced to cancel the hot spot.

[0064] In a preferred embodiment, temperature distribution on theheating face of the ceramic substrate is observed, so that the first andsecond regions are provided based on the observed temperaturedistribution.

[0065] In a preferred embodiment, a cold spot observed on the heatingface is projected onto the back face to define a projected area, onwhich the second region having a smaller emissivity of thermal radiationis provided. Alternatively, a hot spot observed on the heating face isprojected onto the back face to define a projected area, on which thefirst region having a larger emissivity of thermal radiation isprovided.

[0066] When a cold spot is observed in the outer peripheral portion onthe heating face, the second region having a smaller emissivity ofthermal radiation is provided on the side face of the substrate. When ahot spot is observed in the outer peripheral portion on the heatingface, the first region having a larger emissivity of thermal radiationis provided on the side face of the substrate.

[0067] The difference of the center line average surface roughness Ra ofthe first region and that of the second region may preferably be notsmaller than 0.05 μm and more preferably be not smaller than 0.1 μm, onthe viewpoint of the effects according to the present invention.

[0068] The center line average surface roughness Ra of the first regionmay preferably be not smaller than 0.6 μm and more preferably be notsmaller than 0.8 μm, on the viewpoint of the effects according to thepresent invention.

[0069] The center line average surface roughness Ra of the second regionmay preferably be not larger than 0.6 μm and more preferably be notlarger than 0.4 μm, on the viewpoint of the effects according to thepresent invention.

[0070] The average surface roughness is measured by means of a surfaceroughness tester.

[0071] For providing a difference between the center line averagesurface roughness of the first region and that of the second region, thefollowing methods may be listed.

[0072] (1) A part of the surface of the substrate (other than heatingface) is subjected to a roughening treatment to provide the first regionhaving a larger roughness and to leave an untreated second region.

[0073] (2) A part of the surface of the substrate is subjected to asmoothening treatment to provide the second region having a smallerroughness and to leave an untreated first region.

[0074] (3) One part of the surface of the substrate is subjected to aroughening treatment to provide the first region having a largerroughness and the other part of the surface is subjected to asmoothening treatment to provide the second region having a smallerroughness.

[0075] The roughening treatment for providing the first region is notlimited and may preferably be blasting or etching. The followings areparticularly preferred conditions.

[0076] (Sandblast)

[0077] A blasting material for sandblasting may preferably be a ceramicmaterial such as silicon carbide or alumina. Metals are not preferablebecause they may be a source of metal contamination. The particlediameter of the blast material may preferably be smaller than #180, forreducing damage caused on the surface of the ceramic substrate and thecontent of residual metal components on the damaged area. The blastnozzle material may preferably be a ceramic material. Wet and dryprocesses are both available.

[0078] (Etching)

[0079] Wet etching using hydrofluoric acid, hydrochloric acid, nitricacid or ammonia is preferred. Alternatively, dry etching using a halogengas such as NF₃, Cl₂ and ClF₃ is preferred.

[0080] The smoothening treatment for providing the second region is notalso limited and may preferably be mechanical working process. Suchworking includes lapping and polishing. The followings are particularlypreferred conditions.

[0081] ◯ Grinding using diamond grind stones of #800 or more

[0082] ◯ Baffing using free abrasive grains (having a particle size ofnot more that 0.1 μm) such as alumina and colloidal silica grains

[0083] ◯ Lapping using diamond abrasive grains having a particle size ofnot more than 5 μm (number of revolution is not smaller than 10 rpm andpressure is not lower than 100 g/cm²)

[0084] A system for observing the temperature distribution on theheating face is not limited and may preferably be an infraredthermoviewer, a wafer equipped with a thermocouple, an RTD wafer or athermocouple. It is known a method for producing a mask based on theresults of image processing of the observed temperature distribution.

[0085] A material for the substrate is not particularly limited. Thematerial may be a known ceramic material including a nitride ceramicssuch as aluminum nitride, silicon nitride, boron nitride and sialon, andan alumina-silicon carbide composite material. The material may mostpreferably be aluminum nitride or alumina for providing highanti-corrosion property to a corrosive gas such as a halogen based gas.

[0086] The shape of the substrate is not particularly limited, and maypreferably be a disk. Pocket shaped parts, emboss-shaped parts, orgrooves may be formed on its semiconductor mounting face.

[0087] The heater may be produced by any method not particularlylimited, and may preferably be produced by hot pressing or hot isostaticpressing.

[0088] The shape of the resistance heat generator may be coil, ribbon,mesh, plate or film. The material of the heat generator may preferablybe a pure metal selected from the group consisting of tantalum,tungsten, molybdenum, platinum, rhenium and hafnium, or an alloy of twoor more metals selected from the group consisting of tantalum, tungsten,molybdenum, platinum, rhenium and hafnium. When the substrate is made ofaluminum nitride, the material for the heat generator may preferably bemolybdenum or the alloy of molybdenum. The other known resistance heatgenerator of a conductive material such as carbon, TiN, TiC or the likemay be used.

[0089]FIG. 6 is a perspective view showing a heating apparatus 22according to one embodiment of the present invention observed from aback face 2 b. FIG. 7 is a cross sectional view showing the heatingapparatus 22.

[0090] The heating apparatus 22 has a ceramic heater 1B and a supportingmember 21. The heater 1B is the same as that shown in FIG. 5. Asubstrate 2 has a heating face 2 a functioning as a semiconductormounting face for mounting a semiconductor W. One end face 21 c of thesupporting member 21 is joined with the back face 2 b of the heater 1B.The method for joining is not particularly limited. The joining may becarried out by soldering or solid phase welding as described in Japanesepatent publication P8-73280A. The heater and supporting member may bejoined and sealed using a sealing member such as an O-ring and a metalpacking.

[0091] The supporting member 21 has a cylindrical shape. The supportingmember 21 defines an inner space 19 separated from atmosphere 20 in achamber. Power supply means 18 are contained in the inner space 19. Oneends of the power supply means 18 are connected with the terminals 17.21 a denotes an outer surface and 21 b denotes an inner surface of thesupporting member 21. The terminals 17 and power supply means 18 arecontained in the inner space 19 of the supporting member so that theyare prevented from the contact with the atmosphere 20 in a system forproducing semiconductors. It is thereby possible to prevent or reducethe corrosion of the terminals 17 and power supply means 18 so as toprevent the metal contamination of a semiconductor.

[0092] A material for the supporting member is not limited, and includesa known ceramic material including a nitride ceramics such as aluminumnitride, silicon nitride, boron nitride and sialon, and analumina-silicon carbide composite material.

[0093] The shape of each of the first and second power supply means isnot particularly limited, and may be a rod shaped body, a wire shapedbody or a combination of rod and wire shaped bodies. A material for thepower supply means is not particularly limited. The power supply meansare separated from atmosphere 20 in a chamber and thus do not directlyexposed to a highly corrosive substance. The material of the supplymeans may thus preferably be a metal and most preferably be nickel.

[0094] FIGS. 8(a), 8(b), and 9 are cross sectional views each showing anessential part of each ceramic heater 1C, 1D or 1E according to anotherembodiment of the present invention.

[0095] In a ceramic heater 1C of FIG. 8(a), the second region 13 is asmoothened surface described above. Many V-shaped grooves 24 are formedin parallel with each other at predetermined intervals in the firstregion 15. The emissivity of thermal radiation from the first region 15is thereby made larger than that from the second region 13 after theabove smoothening treatment.

[0096] In a ceramic heater ID of FIG. 8(b), the second region 13 is asmoothened surface. Many dimple-shaped or emboss-shaped protrusions 25are formed at predetermined intervals in the first region 15. Theemissivity of thermal radiation from the first region 15 is thereby madelarger than that from the smoothened second region 13.

[0097] In a heater 1E of FIG. 9, the second region 13 is a smoothenedsurface. In the first region 15, the surface area of the substrate isremoved by grinding so that a ground surface 26 is exposed. The groundsurface 26 has a lightness lower than those of smoothened surfaces 10Aand 10B, so that the emissivity of thermal radiation from the region 15is made larger than that from the region 13. When the lightness of thesurface of a ceramic substrate may be changed by working the surface asdescribed above, the lightness of the substrate surface may becontrolled only by working so that the emissivity of thermal radiationmay be controlled.

EXAMPLES

[0098] A ceramic heater was produced according to the method describedreferring to FIGS. 1 to 5. The substrate 2 was composed of an aluminumnitride sintered body having a diameter  of 250 mm and a thickness of10 mm. Heat generators 3A and 3B each having a shape of coil spring andmade of molybdenum are embedded in the substrate 2. Each terminal wasmade of molybdenum and cylindrical shaped.

[0099] Power was supplied to the ceramic heater 1 until the averagetemperature on the heating face 2 a reached about 700° C. Thetemperature distribution on the heating face 2 a was then measured bymeans of a thermoviewer. The results were shown in FIG. 10. As can beseen from FIG. 10, a cold spot 7 having a shape of an arc as shown inFIG. 2(a) was observed. The difference of the maximum and minimumtemperatures on the heating face was measured and proved to be 8.5° C.

[0100] As shown in FIG. 3, the whole of the side face 2 c and back face2 b were lapped to provide smoothened surfaces 10A, 10B and 10C eachhaving a center line average surface roughness of 0.5 μm.

[0101] Masks 12A and 12B were set as shown in FIG. 4 and the smoothenedsurfaces are subjected to sandblasting. The masks were then removed toobtain a ceramic heater 1B shown in FIG. 5. The first region 13 has acenter line average surface roughness of 0.5 μm, and the second region15 has that of 1.0 μm.

[0102] Power was supplied to the ceramic heater 1B until the averagetemperature on the heating face 2 a reached about 700° C. Thetemperature distribution on the heating face 2 a was then measured bymeans of a thermoviewer. The results were shown in FIG. 11. As can beseen from FIG. 11, the cold spot 7 shown in FIG. 10 was not observed.The difference of the maximum and minimum temperatures on the heatingface was measured and proved to be 4.5° C.

[0103] As described above, the present invention provides a novelceramic heater having a ceramic substrate and a heat generator so thatthe temperature on the heating face may be controlled without thenecessity of a temperature controlling member separate from thesubstrate.

[0104] The present invention has been explained referring to thepreferred embodiments. However, the present invention is not limited tothe illustrated embodiments which are given by way of examples only, andmay be carried out in various modes without departing from the scope ofthe invention.

1. A ceramic heater comprising a heat generator and a ceramic substratehaving a surface, said surface including a heating face, a first regionprovided out of said heating face and a second region provided out ofsaid heating face, wherein said second region has an emissivity ofthermal radiation lower than that of said first region.
 2. The heater ofclaim 1, wherein said second region has a center line average surfaceroughness smaller than that of said first region.
 3. The heater of claim1, wherein said surface includes a back face, and said first and secondregions is provided on said back face.
 4. The heater of claim 1, saidsurface includes a side face, and at least one of said first and secondregions is provided on said side face.
 5. The heater of claim 1, whereinat least one of said first and second regions is subjected to a chemicalsurface treatment.
 6. The heater of claim 5, wherein said chemicalsurface treatment is etching.
 7. The heater of claim 1, wherein at leastone of said first and second regions is subjected to a physical surfacetreatment.
 8. The heater of claim 7, wherein said physical surfacetreatment is grinding, lapping, polishing or blasting.
 9. The heater ofclaim 1, wherein said first region has a lightness lower than that ofsaid second region.
 10. The heater of claim 1, wherein a differencebetween the maximum temperature and minimum temperatures on said heatingface is not larger than 20° C. when the average temperature on saidheating face is 600° C.
 11. A heating apparatus for a system forproducing semiconductors, said apparatus comprising said heater of claim1 having a back face, a terminal connected with said generator, a hollowsupporting member defining an inner space and fixed on said back face ofsaid heater, and a power supply means provided in said inner space andelectrically connected with said terminal.
 12. A method for producing aceramic heater comprising a heat generator and a ceramic substratehaving a surface including a heating face, the method comprising thestep of providing a first region on said surface out of said heatingface and a second region on said surface out of said heating face,wherein said second region has an emissivity of thermal radiation lowerthan that of said first region.
 13. The method of claim 12, furthercomprising the step of measuring temperature distribution on saidheating face of said heater, wherein said first and second regions areprovided based on said temperature distribution measured.
 14. The methodof claim 13, wherein said surface includes a back face, a cold spot isdetected on said heating face, and said second region is provided onsaid back face and in a projected zone defined by projecting said coldspot on said back face.
 15. The method of claim 13, wherein said surfaceincludes a back face, a hot spot is detected on said heating face, andsaid first region is provided on said back face and in a projected zonedefined by projecting said hot spot on said back face.
 16. The method ofclaim 12, wherein said second region has a central line average surfaceroughness smaller than that of said first region.